The present invention relates to a thermoplastic resin composition. More particularly, it relates to a thermoplastic resin composition having excellent mechanical strength and heat resistance as well as fine electrical properties such as conductivity and antistatic properties.
It is widely practiced in the art to incorporate an electroconductive material in an electrically insulating thermoplastic resin to provide it with specific properties such as conductivity and antistatic properties, and a variety of conductive materials have been proposed for this purpose. Among the generally used conductive materials are ionic surfactants, nonionic surfactants, organic compounds having polyethylene glycol units or ionic functional groups, such as high polymeric antistats, and inorganic materials such as carbon black, carbon fiber, metallic fiber, metallic powder and metal oxides. In particular, carbon black is used for obtaining high conductivity at a small mixing rate. Further, in order to obtain a high-conductivity blended resin composition, a method has been proposed in which carbon black is compounded in a high concentration or a high density or homogeneously in the resin constituting the sea phase (matrix phase or continuous phase) in the micro structure of a resin blend.
These resin compositions, however, although provided with conductivity, are forced to sacrifice some of the innate advantageous properties of thermoplastic resins, such as molding workability, mechanical strength (particularly toughness) and surface appearance. On the other hand, with the advancement of miniaturization, integration and precision of OA equipment and electronic devices, the request from the market for the minimized tendency of the conductive resin-made electric and electronic parts to collect dust and dirt is becoming more and more serious every year. This request is particularly strong on IC chips used for semiconductors, wafers and interior components of hard discs used for computers, for which it is essential to afford antistatic properties to perfectly prevent collection of dust and dirt.
For such purposes, conductive resin materials, for example, alloys mainly composed of polycarbonate resin (such as polycarbonate resin and ABS resin blend) and alloys mainly composed of polyphenylene ether-based resin (such as polyphenylene ether resin and polystyrene resin blend) are used. These conductive resin materials, however, have the disadvantage of being lowered in mechanical strength and fluidity as a large amount of carbon black must be blended for providing high conductivity to the molding resin material.
For coating of automobile parts, there is generally used “static coating” in which a conductive resin molded part to be coated is electrified and a coating material charged with the opposite polarity is sprayed to the said part. This coating method makes use of the attractive force generated between the molded part surface and the coating material by charging them with opposite polarities to strengthen adhesion of the coating material to the part surface. Polycarbonate resin and polyester resin blends and polyphenylene resin and polyamide resin blends are prevalently used for automobile exterior trim parts and outer plate parts. However, these molding resin materials also have the problem of reduced mechanical strength and fluidity because of mixing of a conductive material for providing conductivity to the resin materials.
As a molding resin material freed of the above problems, Japanese Patent Application Laid-Open (KOKAI) No. 2-201811 discloses a resin material having its conductivity improved by the addition of a small amount of carbon black by selectively containing it in the sea phase in the micro structure of a resin blend, but this resin material is still not cleared of the problem of reduced molding workability. Japanese Patent Application Laid-Open (KOKAI) No. 10-204305 teaches that molding workability and surface appearance can be improved by selectively containing a conductive material such as carbon black in the island phase, i.e. discontinuous phase in the micro structure of a resin blend, but the composition is still unsatisfactory in volume resistivity.